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Abstract:

A propeller (10,110) has a hub (20,120) with blades (40,140). A safety
member (50,150) is provided along at least a portion of the leading edge
(43,143) of each blade (40,140); and the blades (140) may incorporate
anti-cavitation slots (160).

Claims:

1. A safety propeller, preferably for watercraft, of the type having a hub
and a plurality of blades, where each blade has a leading edge extending
from a proximal end of the blade adjacent the hub to a distal end spaced
from the hub; anda respective safety member is provided over at least 50%
of the leading edge of each blade, each safety member being of greater
thickness and/or height than the leading edge, and at least a portion of
the safety member extends from a thrust or driving face of the blade in
the forward direction of rotation of the propeller.

2. A propeller as claimed in claim 1, wherein:for a propeller which
rotates in a clockwise direction (when viewed from a trailing end of the
hub), the safety member on each thrust or driving face of the blade
appears to be directed towards the trailing end of the propeller.

3. A propeller as claimed in claim 1, wherein:the safety member extends
over more than 50% of the length of the leading edge of the blade and is
of a greater height so that the safety member will strike any obstruction
before the balance of the leading edge not provided with the safety
member.

4. A propeller as claimed in claim 3, wherein:the safety member is of a
constant height over the leading edge, or of relatively increasing height
towards the distal end of the blade.

5. A propeller as claimed in claim 3, wherein:the safety member is located
with a central axis substantially parallel to, or aligned with, the
leading edge, or with the central axis increasingly leading the leading
edge of the blade in the direction from the proximal end to the distal
end of the blade.

6. A propeller as claimed in claim 5, wherein:the safety member is
smoothly contoured into the adjacent portion of the blade.

7. A propeller as claimed in claim 1, wherein:the safety member is mounted
on, or formed integrally with, the blade.

8. A propeller as claimed in claim 1, wherein:at least one anti-cavitation
slot is provided in each blade.

10. A propeller as claimed in claim 9, wherein:the or each side wall of
the anti-cavitation slot extends through blade substantially parallel to
the rotational axis of the propeller.

11. A propeller, preferably for watercraft, of the type having a hub and a
plurality of blades, where each blade has a respective leading edge and a
trailing edge extending from respective proximal ends of the blade
adjacent the hub to a distal end spaced from the hub; wherein:at least
one anti-cavitation slot extends through each blade, spaced from the
respective leading edge and trailing edge of the blade.

12. A propeller as claimed in claim 11, wherein:the or each
anti-cavitation slot is of circular, square, rectangular,
modified-rectangular or other shape in plan view.

13. A propeller as claimed in claim 12, wherein:the, or each, side wall of
each anti-cavitation slot lies substantially parallel to the rotational
axis of the hub.

14. A propeller as claimed in claim 11, wherein:the, or each,
anti-cavitation slot is spaced at least 50% of the distance between the
leading edge and the trailing edge of the blade, measured at the hub.

15. A propeller as claimed in claim 11, wherein:the, or each,
anti-cavitation slot is spaced 20% to 70% of the distance from the hub to
the distal end of the blade.

16. A propeller as claimed in claim 12, wherein:for the anti-cavitation
slots of square, rectangular and modified shape, the opposed side walls
of the anti-cavitation slots extend substantially parallel to a central
axis of the slots extending substantially radially from the hub.

17. A propeller, preferably for watercraft, of the type having a hub and a
plurality of blades, where each blade has a leading edge extending from a
proximal end of the blade adjacent the hub to a distal end spaced from
the hub;a respective safety member is provided over at least 50% of the
leading edge of each blade, each safety member being of greater thickness
and/or height than the leading edge, and at least a portion of the safety
member extends from a thrust or driving face of the blade in the forward
direction of rotation of the propeller; andat least one anti-cavitation
slot extends through each blade, spaced from the respective leading edge
and trailing edge of the blade.

18. (canceled)

Description:

BACKGROUND OF THE INVENTION

[0001]THIS INVENTION relates to a safety propeller.

[0002]The invention is particularly suitable for, but not limited to, a
safety propeller for watercraft.

[0003]The term "watercraft" will include boats as small as dinghies or
tenders fitted with outboard motors; through pleasure boats and
speedboats with inboard/outboard motors; up to large ships such as cargo
ships, tankers and military vessels.

PRIOR ART

[0004]Rotating watercraft propellers have always been a source of danger
for persons (eg., skiers) or animals (eg., dugongs or other sea
creatures) which come into contact with them.

[0005]Furthermore, in shallow waters, the propeller blades tend to dig
into the river-, lake- or seabeds, both damaging the propellers and
causing environmental damage to the beds.

[0006]One solution to minimise the problem has been the development of
so-called "ring propellers" which have a continuous, or interrupted, ring
around the distal ends, of the blade to prevent, or minimise, contact
between the leading edges of the blades and any obstruction. However,
such ring propellers generally have significantly minimised performance
when operating in reverse.

SUMMARY OF THE PRESENT INVENTION

[0007]It is an object of the present invention to provide a safety
propeller, preferably for watercraft, where any damage to any obstruction
by the leading edges of the blades of the propeller is minimised.

[0008]It is a preferred object of the present invention to provide such a
safety propeller where safety members are formed integrally with, or are
fitted to, the leading edges of the blades.

[0009]It is a further preferred object of the present invention to provide
such a propeller where the position of the safety members has little, if
any, negative effect on the performance of the propeller when compared to
conventional propellers.

[0010]It is a still further preferred object to provide such a propeller
where minimal, if any, damage occurs to the blades when they strike an
obstruction.

[0011]It is a still further preferred object to provide such a propeller
with anti-cavitation slots in the blades to maximise the performance of
the propeller.

[0012]Other preferred objects of the present invention will become
apparent from the following description.

[0013]In one aspect, the present invention resides in:

[0014]a safety propeller, preferably for watercraft, of the type having a
hub and a plurality of blades, where each blade has a leading edge
extending from a proximal end of the blade adjacent the hub to a distal
end spaced from the hub; and

[0015]a respective safety member is provided over at least 50% of the
leading edge of each blade, each safety member being of greater thickness
and/or height than the leading edge, and at least a portion of the safety
member extends from a thrust or driving face of the blade in the forward
direction of rotation of the propeller.

[0016]NB: For a propeller which rotates in a clockwise direction, (when
viewed from the trailing end of the hub), the safety member on each
thrust or driving face of the blade appears to be directed towards the
trailing end of the propeller.

[0017]Preferably, the safety member extends over more than 50% of the
length of the leading edge of the blade and is of a greater height so
that the safety means will strike any obstruction before the balance of
the leading edge not provided with the safety member.

[0018]While the safety member may be of a constant height over the leading
edge, it may be of relatively increasing height towards the distal end of
the blade.

[0019]While the safety member may be located with a central axis
substantially parallel to, or aligned with, the leading edge, it is
preferable that the central axis increasingly leads the leading edge of
the blade in the direction from the proximal end to the distal end of the
blade.

[0020]Preferably, the safety member is smoothly contoured into the
adjacent portion of the blade.

[0021]The safety member may be mounted on (eg., by welding or brazing), or
formed integrally with, the blade.

[0022]The relative height of the safety member to the leading edge of the
blade; the relative thickness of the safety member to the thickness of
the blade; and/or the relative degree by which the central axis of the
safety member leads the leading edge of the blade, may be varied to suit
the particular intended application for the safety propeller.

[0023]Preferably, at least one anti-cavitation slot is provided in each
blade.

[0024]Each cavitation slot may be of circular, square, rectangular or
modified rectangular (ie., a rectangle with semi-circular ends) shape in
plan view.

[0025]Preferably, the or each side wall of the anti-cavitation slot
extends through blade substantially parallel to the rotational axis of
the propeller.

[0026]In a second aspect, the present invention resides in a propeller,
preferably for watercraft, of the type having a hub and a plurality of
blades, where each blade has a respective leading edge and trailing edge
extending from respective proximal ends of the blade adjacent the hub to
a distal end spaced from the hub; wherein:

[0027]at least one anti-cavitation slot extends through each blade, spaced
from the respective leading edge and trailing edge of the blade.

[0028]The or each anti-cavitation slot may be of circular, square,
rectangular, modified-rectangular (ie., a rectangle with semi-circular
ends) or other shape in plan view.

[0029]Preferably, the, or each, side wall of each anti-cavitation slot
lies substantially parallel to the rotational axis of the hub.

[0030]Preferably, the, or each, anti-cavitation slot is spaced at least
50% of the distance between the leading edge and the trailing edge of the
blade, measured at the hub.

[0031]Preferably, the, or each, anti-cavitation slot is spaced 20% to 70%
of the distance from the hub to the distal end of the blade.

[0032]Preferably, for the anti-cavitation slots of square, rectangular and
modified shape, the opposed side walls of the anti-cavitation slots
extend substantially parallel to a central axis of the slots extending
substantially radially from the hub.

[0033]In a third aspect, the present invention resides in a safety
propeller of the first aspect, which incorporates the anti-cavitation
slots of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]To enable the invention to be fully understood, preferred
embodiments will now be described with reference to the accompanying
drawings, in which:

[0035]FIGS. 1 and 2 are respective front and rear elevations of a first
embodiment of a propeller in accordance with the present invention;

[0036]FIGS. 3 and 4 are respective perspective and side elevational views
of the first embodiment;

[0037]FIG. 5 is a front perspective view of the first embodiment showing
the sectional view of one blade on lines A-A to E-E respectively;

[0038]FIG. 6 is a front view of a second embodiment of a propeller in
accordance with the present invention;

[0039]FIGS. 7 and 8 are respective perspective and side elevational views
of the second embodiment;

[0041]FIG. 10 is a front elevational view showing three (3) alternative
shapes for the anti-cavitation slots of the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042]In the first embodiment illustrated in FIGS. 1 to 5, an "off the
shelf" propeller has had each of its 3 blades modified to incorporate the
safety members of the present invention.

[0043]It will be readily apparent to the skilled addressee that the safety
members may be manufactured integrally with the blades; and that the
number, size and shape of the blades on the propeller will be dependent
on the intended application(s) for the particular safety propeller made
in accordance with the present invention.

[0044]In the specific embodiment illustrated, the propeller 10 has a hub
20 with three (3) equally spaced blades 40, to be hereinafter described
in more detail.

[0045]The hub 20 has an outer tubular body 21 which is outwardly flared to
a trailing end 22.

[0046]An inner tubular body 23 is connected to the outer tubular body 21
by three (3) spaced ribs 24; where the outer body 21, the inner body 23
and the ribs 24 define three (3) exhaust passages 25 through the hub 20.

[0047]The inner body 23 has a tubular vibration damping body 26, which
supports a splined tubular driving body 27 mountable on the output shaft
(not shown) of a suitable power source (eg., an outboard
motor/inboard/outboard drive or the drive shaft or propeller shaft of an
inboard motor).

[0048]Each blade 40 has a curved leading edge 41 with a proximal end 42
adjacent the hub 20 and a distal end 43 at the periphery of the blade 40,
where the distal end 43 leads into the trailing edge 44 of the blade.

[0049]A recess 45 is machined into the leading edge 41 of the blade over
approximately 70-80% of the length of the leading edge. In the specific
example to be hereinafter described, the depth of the recess 45 is
approximately 4-5 mm, where the safety member 50 to be hereinafter
described is formed of a rod or cylinder of 6 mm diameter.

[0050]It will be apparent to the skilled addressee that the depth of the
recess 45 may be as shallow as, eg., 1 mm, so that the relative height of
the safety member 50 relative to the leading edge 41 of the blade 40 may
be varied to suit the particular intended application when the safety
member 50 is made of material of a particular thickness or diameter.

[0051]The safety member 50 in the present example is formed from a length
of 6 mm diameter aluminium rod which is placed in the recess 45, and
where the central axis of the safety member 50 is progressively advanced
forwardly of the leading edge 41 of the blade 40 in the direction from
the proximal end 42 to the distal end 43. (As hereinbefore described, in
side view, the safety member 50 extends to the rear of the thrust or
driving face of the blade 40, ie., towards the trailing end 22 of the hub
20.)

[0052]For a counter-rotating propeller, the propeller will be a
"mirror-image" of the propeller illustrated.

[0053]While it is preferable that the central axis of the safety member 50
progressively extends from the leading edge 41 of the blade 40 in the
direction from the proximal end 42 to the distal end 43, this is not
essential to the invention, and the central axis may be parallel with, or
aligned with, the leading edge 41 of the blade.

[0054]In experiments conducted with the propeller of the first embodiment
illustrated in FIGS. 1 to 5 of the drawings, there has been no loss of
performance in the forward direction compared with the propeller before
modification (and indeed, there has been a minimal increase in speed).
Furthermore, there has been little, if any, loss in efficiency in the
modified propeller when operating in the reverse direction.

[0055]Preferably, the profile of the safety member 50 is "blended" or
"contoured" into the profile of the blade 40 adjacent to the safety
member 50.

[0056]While the safety member 50 in this embodiment has been manufactured
from solid rod, it could be manufactured from, eg., timber or U-section
material.

[0057]It will be readily apparent to the skilled addressee that the safety
member 50 may be formed integrally with each blade at the time of
manufacture.

[0058]The safety member 50 may be manufactured from the same material as
the propeller, such as metal (eg., aluminium), plastics (which may be
fibre-reinforced) "Kevlar" (trade mark), carbon fibre, or other suitable
materials; or may be made from such materials selected, eg., for their
impact strength.

[0059]In experiments conducted in very shallow water, it has been found
that the blades 40 do not cut into the underlying waterbed, but that the
propeller 10 tends to "walk" over the bed until deeper water is reached.
Furthermore, little, if any, damage to the blades 40 (or the safety
member 50) was noted, minimising imbalances in the propeller 10 or
potential sites for blade failure.

[0060]While the safety member 50 can be provided over the full length of
the leading edge of each blade 40, it is preferable that the safety
member 50 extends along such a portion of the leading edge 41 so that the
safety member 50 will strike any obstruction before the remainder of the
leading edge 41 comes into contact therewith.

[0061]If preferred, the safety member 50 may extend past the distal ends
43 of the blades 40 and thereby extend a short distance along the
trailing edges 44.

[0062]FIGS. 6 to 9 illustrate a second embodiment of the propeller 110,
where the three blades 140 (around the hub 120) have a substantially
linear trailing edge 144.

[0063]The safety member 150 extends along the leading edge 143 of each
blade 140 in the manner hereinbefore described with reference to the
first embodiment of FIGS. 1 to 4.

[0064]As illustrated in FIGS. 7 and 8, the safety member 150 extends from
the thrust or driving face 149 of each blade 140 so that, in side view,
it extends from the leading edge 143 of the blade 140 towards the
trailing end 122 of the hub 120.

[0065]In this embodiment, a respective anti-cavitation slot 160 is
provided in each blade 140 approximately mid-point between the leading
and trailing edges 143, 144 and approximately at 50% radial distance from
the hub 120.

[0066]Each anti-cavitation slot 160 has a longitudinal axis which is
substantially radial to the centre line (or axis of rotation) of the hub
120.

[0067]In this embodiment, each anti-cavitation slot 160 is of modified
rectangular shape, with parallel side walls 161, 162 interconnected by
semi-circular end walls 163, 164.

[0068]As shown in FIG. 9, the side walls 161, 162 lie substantially
parallel to the centre line of the hub 120 and are inclined to the
opposed faces of the blade 140.

[0069]In tests conducted on a propeller 110 in accordance with this
embodiment, it has been found that the propeller suffers little, if any,
cavitation over a wide range of operating conditions, thereby minimising
any loss of performance due to cavitation, eg., at high engine R.P.M. or
on sudden acceleration. In addition, the propeller has good performance
in reverse.

[0071]In another alternative, not illustrated, the cavitation slots may be
"hook-shaped" and may follow the shape of the blades.

[0072]The size, shape and location of the anti-cavitation slots 160, 260,
360, 460 on the blades 140, 240, 340, 440 can be varied to suit the
particular intended location.

[0073]In addition, the side walls of the anti-cavitation slots may be
inclined forwardly or rearwardly, or be perpendicular to, the opposed
faces of the blades.

[0074]The propeller 110 has the double advantages of the safety member 150
with the anti-cavitation slots 160 to provide a propeller which is safe
in operation and with no loss of, or even improved, performance, compared
to existing propellers.

[0075]Various changes and modifications may be made to the embodiments
described and illustrated without departing from the present invention
defined in the appended claims.